European patent application EP-A-0 686 468 discloses a method of manufacturing lipstick sticks.
That known method uses a flexible mold which is thermally conditioned prior to introducing therein a predetermined quantity of a composition in the molten state for constituting a lipstick stick after it has cooled and solidified.
The stick is unmolded in two stages.
In a first stage, suction is applied to the outside of the mold, but at its top end only, so as to cause said top end to expand and provide annular clearance around the stick inside the mold.
This clearance enables the stick to be engaged in an extractor member, e.g. constituted by the cup of a lipstick case, while the bottom portion of the stick continues to be held by the mold.
In a second stage, once the extractor member has been engaged on the stick, suction is exerted on the outside of the mold over its entire height so as to separate the bottom portion of the stick from the mold, thereby facilitating removal of the stick.
The material selected for making the mold must satisfy various requirements, and in particular:
it must be physically and chemically compatible with the stick-constituting composition;
it must withstand the temperature of said composition in the molten state, i.e. about 100° C.;
it must withstand the mechanical and thermal stresses to which it is subjected during a stick-manufacturing cycle; and
it must be dimensionally stable.